The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae.
The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together. The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae. While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle “S” shape. If the proper shaping and/or curvature are not present due to scoliosis, neuromuscular disease, cerebral palsy, or other disorder, it may be necessary to straighten or adjust the spine into a proper curvature.
Generally the correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws and rods. Often, prior to inserting a screw, a bore may be drilled and tapped to receive the screw. The screws may be inserted into the pedicles of the vertebrae to act as bone anchors, and the rods may be inserted into heads of the screws. Two rods may run substantially parallel to the spine and secure the spine in the desired shape and curvature. Thus the rods, which are shaped to mimic the correct spinal curvature, force the spine into proper alignment. Bone grafts are then placed between the vertebrae and aid in fusion of the individual vertebrae together to form a correctly aligned spine.
A surgical screwdriver may be used to insert a screw into the vertebra. The screwdriver typically includes a driving end with a driving feature and a handle portion for applying torque to the screw. The driving feature typically includes a geometry corresponding to a recess or receiving feature of the screw. The driving feature may frictionally or compressively engage the screw to temporarily attach to the screwdriver during insertion into the vertebrae. In some cases, a threaded section of the screwdriver may be used to engage with the heads on the screws. For example, the driving feature may be aligned with the receiving feature of the screw and the threaded section may be threaded onto the mating threads in the head of the screws.
During a surgical procedure, a surgeon, assistant, or nurse may need to attach numerous screws to screwdrivers prior to insertion into a surgical area. In some cases, the driving feature may not provide sufficient friction forces or compressive forces to hold the screw in place as the screwdriver is transferred to the surgeon during the surgical procedure. Screws may fall off of the screwdriver causing delays and risk of contamination. In other cases, the screwdriver may be difficult to align with the screw and head. The driving feature may need to be aligned with the receiving feature prior to threading the threaded section onto the mating threads of the head. Therefore, a screwdriver that provides secure, quick, and reliable attachment of the screw is needed.